Re: [Boost-users] lexical_cast causes level 4 warnings w/ VC7.1

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-11-21 09:09:21

Sam Partington wrote:
> Peter Dimov <mailto:pdimov_at_[hidden]> wrote:
>> Sam Partington wrote:
>>>
>>> 4511 and 4512 are useless warnings.  They are telling you that the
>>> copy constructor and assignment operator are inaccessible.  Even
>>> though you're not trying to call them. [...]
>>
>>> C4127 is also awkward.  As it gives warnings for some common idioms.
>>> It refers to conditional expressions being constant.
>>
>> These warnings can be annoying, but they aren't useless. They do find
>> bugs.
>
> I agree that 4127 can help you find bugs.  But I can't think of any
> situation where 4511 or 4512 will help you find a bug.  If you actually
try
> to call an inaccesible copy constructor or assignement operator, then the
> compiler (correctly) fails to compile it.
>
> Thats why I used the word "awkward" rather than "useless" for 4127.
>
> I'll happily be proved wrong though.

I can't recall a specific example at the moment, though I have definitely
encountered one several times.

The basic idea is that 4511/4512 help you enforce the guideline that a class
should always either have a declared copy constructor and an assignment
operator, or a comment that says "implicit versions are fine and useful".
This guideline _does_ eliminate bugs by forcing programmers to think clearly
about the copy semantics of every class that they write. With this in mind,
every 4511/4512 indicates a violation of this guideline (because the
implicit versions are obviously neither fine nor useful), and many
violations are bugs ( the guideline would be useless if this weren't so
;-) ).

This guideline is not universally accepted. Some prefer the ": noncopyable"
idiom, or some equivalent thereof. If you don't buy it, you will likely find
451[12] useless. Your choice.